Linearity for field weakening in an interior permanent magnet machine

ABSTRACT

Systems and methods are disclosed to provide torque linearity in the field-weakening region for an electric (e.g., IPM) machine. The systems and methods implement a field weakening and a torque linearity control loop for linearizing torque generated by an electric machine. As a result, torque linearity is maintained when the electric machine operates in the field weakening region.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.11/829,298, filed Jul. 27, 2007.

TECHNICAL FIELD

Embodiments of the present invention relate generally to electricmachine control, and more particularly relate to techniques that affecttorque linearity in a field weakening region of an electric machine.

BACKGROUND

An electric machine converts electrical power into mechanical force andmotion. Electric machines are found in numerous applications includinghousehold appliances such as fans, refrigerators, and washing machines.Electric drives are also increasingly used in electric andhybrid-electric vehicles.

A rotary electric machine generally has an internal rotating magnet,called the rotor, which revolves inside a stationary stator. Theinteraction between the rotor electromagnetic field with the fieldcreated by the stator winding creates the machine torque. The rotor maybe a permanent magnet or it may be made of coils. However, if the rotorhas permanent magnets embedded therein (i.e., the permanent magnets arenot in the rotor surface), the electric machine may be referred to as aninterior permanent magnet (IPM) machine. The part of the machine acrosswhich the input voltage is supplied is called the “armature”. Dependingupon the design of the machine, either the rotor or the stator can serveas the armature. In an IPM machine, the armature is the stator, and is aset of winding coils powered by input voltage to drive the electricmachine.

The reverse task of converting mechanical energy into electrical energyis accomplished by a generator or dynamo. An electrical machine asmentioned above may also function as a generator since the componentsare the same. When the machine/generator is driven by mechanical torque,electricity is output. Traction machines used on hybrid and electricvehicles or locomotives often perform both tasks.

Typically as an electric machine accelerates, the armature (and hencefield) current reduces in order to keep stator voltage within itslimits. The reduction in field which reduces magnetic flux inside themachine is also called flux or field weakening. Field weakening controltechniques can be used to increase performance in the torque-speedcharacteristic of the machine. To retain control of stator current, themachine field may be reduced by a field weakening control loop. Thefield or flux weakening in an IPM machine can be accomplished byadjusting the stator excitation. Stator excitation in an IPM machine maybe controlled by voltage pulse width modulation (PWM) of a voltagesource inverter.

Flux weakening techniques have been used in the past where IPM flux ispurposely made weak to reduce the problems associated with high flux,such as over voltage due to high Back-EMF. For example, during aconstant torque region of operation of an electric machine, closed loopcurrent regulator control has been used to control the applied PWMvoltage excitation so that the instantaneous phase currents follow theircommanded values. However, saturation of the current regulators mayoccur at higher speeds when the machine terminal voltage approaches themaximum voltage of the PWM inverter. Beyond this point, the flux shouldbe weakened to maintain proper current regulation up to the maximumavailable machine speed. Reducing the magnetic flux inside the machineprovides improved power characteristics of the IPM machine at highspeeds. However, torque may decrease in direct proportion to the flux.

Accordingly, it is desirable to keep torque linearity in thefield-weakening region for an IPM machine within the voltage and currentsystem constraints. Furthermore, other desirable features andcharacteristics will become apparent from the subsequent detaileddescription and the appended claims, taken in conjunction with theaccompanying drawings and the foregoing technical field and background.

BRIEF SUMMARY

Systems and methods are disclosed to provide torque linearity in thefield-weakening region for an electric (e.g., IPM) machine. The systemsand methods implement a field weakening and a torque linearity controlloop for linearizing torque generated by an electric machine. First andsecond voltage commands are used at the field weakening loop to generatea first adjusting current command. The first adjusting current commandis then provided to the torque linearity control loop, where it ismultiplied by a gain to generate an output current command, which canthen be limited to generate a second adjusting current command. Thesecond adjusting current command can then be added to a current commandto generate an adjusted current command. The first adjusting currentcommand can also be added to another current command to generate anotheradjusted current command. The adjusted current commands and feedbackcurrents are then used at a synchronous current regulator to generatenew first and second voltage commands. As a result, torque linearity ismaintained when the electric machine operates in the field weakeningregion.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure will hereinafter be described inconjunction with the following drawing figures, wherein like numeralsdenote like elements, and

FIG. 1 is a functional block diagram that includes an existing controlsystem without a torque linearity block for a vector controlled IPMmachine;

FIG. 2 is a functional block diagram of a control system with a torquelinearity control block for a vector controlled IPM machine;

FIG. 3 is a functional block diagram of a phase current limit module ofthe control system of FIG. 2;

FIG. 4 illustrates current regulation performance for an IPM machinewith and without the torque linearity control block; and

FIG. 5 is a flowchart illustrating a process for operating an electricmachine with a torque linearity control block.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. Furthermore, there is no intention to be bound by anyexpressed or implied theory presented in the preceding technical field,background, brief summary or the following detailed description.

Embodiments of the invention may be described herein in terms offunctional and/or logical block components and various processing steps.It should be appreciated that such block components may be realized byany number of hardware, software, and/or firmware components configuredto perform the specified functions. For example, an embodiment of theinvention may employ various integrated circuit components, e.g., memoryelements, controlled switches, digital signal processing elements, logicelements, look-up tables, or the like, which may carry out a variety offunctions under the control of one or more microprocessors or othercontrol devices. In addition, those skilled in the art will appreciatethat embodiments of the present invention may be practiced inconjunction with any number of vehicle applications and that the systemdescribed herein is merely one example embodiment of the invention.

For the sake of brevity, conventional techniques and components relatedto vehicle electrical parts and other functional aspects of the system(and the individual operating components of the system) may not bedescribed in detail herein. Furthermore, the connecting lines shown inthe various figures contained herein are intended to represent examplefunctional relationships and/or physical couplings between the variouselements. It should be noted that many alternative or additionalfunctional relationships or physical connections may be present in anembodiment of the invention.

The following description may refer to elements or nodes or featuresbeing “connected” or “coupled” together. As used herein, unlessexpressly stated otherwise, “connected” means that oneelement/node/feature is directly joined to (or directly communicateswith) another element/node/feature, and not necessarily mechanically.Likewise, unless expressly stated otherwise, “coupled” means that oneelement/node/feature is directly or indirectly joined to (or directly orindirectly communicates with) another element/node/feature, and notnecessarily mechanically. Thus, although the schematic shown in FIG. 2depicts an example arrangement of elements, additional interveningelements, devices, features, or components may be present in anembodiment of the invention (assuming that the functionality of thesystem is not adversely affected).

Embodiments of the invention are described herein in the context of onepractical non-limiting application, namely, a control system for an IPMmachine. In this context, the example technique is applicable tooperation of a system suitable for a hybrid vehicle. Embodiments of theinvention, however, are not limited to such vehicle applications, andthe techniques described herein may also be utilized in other electricpowered control applications.

FIG. 1 is a functional block diagram that depicts an existing controlsystem 100 for a vector controlled IPM machine suitable for use with ahybrid vehicle. Such systems are well known and, therefore, theoperation of system 100 will not be described in detail here. Insummary, control system 100 adjusts the q-axis component of the statorcurrent command I_(Q)* (q-axis current command) of the IPM machine usinga flux weakening control loop. Control system 100 includes: a currentcommand 3-D table lookup module 102, a synchronous current regulatormodule with dynamic over modulation 116, a DC to AC transformationmodule 118, a PWM inverter 120, an AC to DC transformation module 122,an IPM machine 124, and a field weakening module 114. Control system 100operates as described below.

Based on a torque command T*, the rotor rotational speed ω_(R), and aDC-link voltage V_(DC), optimal current commands (I_(D)* and I_(Q)*) aregenerated using the current command 3-D table look-up module 102. Theinputs to the table look-up module 102 are provided by a voltage sensorfrom the V_(DC) input to the inverter 120, and a position sensor (notshown in FIG. 1) from the IPM machine 124. The q-axis current commandI_(Q)* is adjusted to obtain an adjusted command (I_(Q)**) as explainedbelow.

The I_(D) and I_(Q) stationary currents (d-axis and q-axis components ofthe stator current) from the IPM machine 124 are fed to the synchronouscurrent regulator module with dynamic over modulation 116, whichgenerates synchronous voltage commands (V_(D)* and V_(Q)*). The commandvoltages V_(D)* and V_(Q)* are vector rotated using the rotor angularposition θ_(R), which is provided by IPM machine 124. The outputs of thecurrent regulator with dynamic over modulation 116 (namely, V_(D)* andV_(Q)*) are fed to the DC to AC transformation module 118 to generatestationary frame voltage commands (V_(AS)* V_(BS)*, and V_(CS)*) basedon V_(D)* and V_(Q)*.

The V_(AS)*, V_(BS)*, and V_(CS)* stationary frame voltage commands arefed to the inverter 120 to generate I_(AS), I_(BS) and I_(CS), which arethe respective stationary frame currents. The inverter 120 may be, forexample, a PWM inverter which applies alternating three phase voltage tothe stator winding of the IPM machine 124.

The IPM machine 124 then operates at the rotational speed ω_(R) based onthe stationary frame currents I_(AS), I_(BS) and I_(CS).

The AC to DC transformation module 122 generates I_(D) and I_(Q) (thed-axis and q-axis components of the stator feedback current) based onI_(AS), I_(BS), I_(CS), and θ_(R). Additional details of the controlsystem 100 can be found in United States Patent Application Number2005/0212471, the content of which is hereby incorporated by referencein its entirety.

The Back-EMF is proportional to the rotational speed, ω_(R). Moreover,the Back-EMF of the electric machine increases as the rotational speedω_(R) of the electric machine is increased. Above a certain rotationalspeed, the voltage of the IPM machine may become higher than the voltageof the bus, resulting in reversal of current flow (regenerating insteadof motoring). To control the I_(D) and I_(Q) components of the statorcurrent, the machine flux is reduced by a field weakening control loop.The field weakening module 114 generates an adjusting current commandΔI_(Q) (ΔI_(Q) is the adjusting q-axis current, (which decreases theflux in the machine but also decreases the torque), based on V_(D)* andV_(Q)* to adjust the current command I_(Q)*. ΔI_(Q) is then added toI_(Q)* by an adder 112 to generate the adjusted current command I_(Q)**.

Adjusting I_(Q)* in this manner results in a decrease in the torque, aswill be explained in the context of FIG. 3. The aforementioned reductionin torque reduces the maximum torque available from the IPM machine, andit may reduce the machine efficiency. Additional details of the fieldweakening control loop module 114 can be found in U.S. patentapplication Ser. No. 11/552,580, filed Oct. 25, 2006, which is herebyincorporated by reference in its entirety.

To keep torque linearity in the field weakening region of an IPMmachine, a torque linearity loop according to an embodiment of theinvention is utilized as explained below.

FIG. 2 is a block diagram that illustrates a control system 200 for avector controlled IPM machine, which is suitable for use in a hybridvehicle. System 200 includes a torque linearity control loop that issuitably configured to perform a torque linearity control functionaccording to an embodiment of the invention. System 200 is suitable foruse with a vehicle having an electric traction machine (e.g., anelectric vehicle or a hybrid vehicle). A practical control system 200may include a number of electrical components, circuits and controllerunits other than those shown in FIG. 2. Conventional subsystems,features, and aspects of the control system 200 will not be described indetail herein. The control system 200 has components that are similar tocontrol system 100 (common features, functions, and elements will not beredundantly described here). For this embodiment, as shown in FIG. 2,the control system 200 generally includes: a current command 3-D tablelookup module 202, a torque linearity module 204, a phase current limitmodule 211, a synchronous current regulator module with dynamic overmodulation 216, a DC to AC transformation module 218, a PWM inverter220, an AC to DC transformation module 222, an IPM machine 224, and afield weakening control loop module 214. System 200 operates with an IPMmachine 224. In particular, inverter 220 drives IPM machine 224.

The torque linearity module 204 generates an adjusting current commandΔI_(D) (ΔI_(D) is the adjusting current in the d-axis, which decreasesthe flux in the machine while torque linearity is maintained), which isbased on ΔI_(Q) as explained below. In practice, ΔI_(Q) is provided bythe field weakening control loop module 214. ΔI_(D) is added by an adder210 to I_(D)* to generate an adjusted current command I_(D)**. Theadjusted current command I_(D)** is fed to the synchronous currentregulator module with dynamic over modulation 216.

For this embodiment, the torque linearity module 204 includes aproportional gain module 206 and a limiter module 208 coupled to theproportional gain module 206. The proportional gain module 206 applies aproportional gain, K, to ΔI_(Q). K may be a constant having a value thattypically ranges from about one to about three, or it may be a variablethat varies as a function of the torque command (T*) and the adjustedcurrent command (I_(Q)***). For example, K may be calculated based onthe following relationship:

${\frac{4}{3*P} \cdot \frac{T^{*}}{\left( {L_{Q} - L_{D}} \right)I_{Q}^{**{*2}}}},$where P is the number of poles of the machine, L_(D) and L_(Q) are thed-axis and q-axis machine inductances, T* is the torque command, andI_(Q)*** is a limited q-axis current command.

ΔI_(Q) is multiplied by K to obtain an output current adjusting command(ΔI_(D)). ΔI_(D) is then fed to the limiter 208 to keep the currentadjusting command ΔI_(D) within its range (about −30 to about 0 AMPS).

To keep the I_(D)−I_(Q) vector within the maximum torque per fluxboundaries, the phase current limit module 211 is used. The phasecurrent limit module 211 is configured to set the maximum phase currentat any DC-voltage V_(DC) and machine rotor speed ω_(R). FIG. 3 is afunctional block diagram that depicts the phase current limit module 211(see FIG. 2). The maximum available current block 230 provides themaximum phase current I_(S(max)) as a function of V_(DD) and ω_(R). Themaximum phase current I_(S(max)) is constant in the constant torqueregion. However, in the field weakening region, I_(S(max)) is decreasedaccordingly to follow the maximum torque per flux machine curve. I_(Q)**is first limited by I_(S(max)) resulting in the limited q-axis currentcommand I_(Q)***. The maximum d-axis current command is calculated asI_(D(max))=√{square root over (I_(S(max)) ²−I_(Q)***²)}. Then, I_(D)**is limited by I_(D(max)) resulting in the limited d-axis current commandI_(D)***.

FIG. 4 illustrates current regulation performance with and without thetorque linearity control block. The field weakening control loop module214 keeps the current regulator stable at the available voltage byadjusting the I_(Q) current by an amount ΔI_(Q) as explained above.ΔI_(Q), however, moves the current vector 310 from point 304 on the T1constant torque curve to point 308 on the T2 constant torque curve,thereby decreasing the torque in direct proportion to the flux. It isdesirable to keep the current vector on the T1 constant torque curve inthe field weakening region of the IPM machine. To this end, the controlloop of the torque linearity module 204 generates ΔI_(D), which movesthe current vector 310 from point 308 on the T2 constant torque curve topoint 306 on the T1 constant torque curve, thereby keeping the torqueconstant and maintaining torque linearity in a field weakening region ofthe IPM machine. The techniques described herein adjust both I_(D) andI_(Q) to decrease flux in the field weakening region, while keepingtorque linearity.

FIG. 5 is a flowchart illustrating a torque linearity operating process400 for an electric, hybrid electric, or fuel cell vehicle. Process 400may be performed by control system 200 as described above. The varioustasks performed in connection with process 400 may be performed bysoftware, hardware, firmware, or any combination thereof. It should beappreciated that process 400 may include any number of additional oralternative tasks, the tasks shown in FIG. 5 need not be performed inthe illustrated order, and process 400 may be incorporated into a morecomprehensive procedure or process having additional functionality notdescribed in detail herein. For illustrative purposes, the followingdescription of process 400 may refer to elements mentioned above inconnection with FIGS. 1-3.

Process 400 adjusts the q-axis and the d-axis components of the statorcurrent commands (I_(D)* and I_(Q)*) of the IPM machine, so torqueremains linear during the field weakening region of the IPM machine,which would otherwise fall proportional to the reduction in the flux. Inpractical embodiments, portions of process 400 may be performed bydifferent elements of control system 200, e.g., the current command 3-Dtable lookup module 202, the torque linearity module 204, the phasecurrent limit module 211, the synchronous current regulator module withdynamic over modulation 216, the DC to AC transformation module 218, thePWM inverter 220, the AC to DC transformation module 222, the IPMmachine 224, and the field weakening control loop module 214.

Torque linearity operating process 400 begins by generating first andsecond current commands (I_(Q)* and I_(D)*) based on a torque commandT*, a rotor angular velocity ω_(R), and a DC-link voltage V_(dc) (task402).

Process 400 also generates an adjusting current command ΔI_(Q) based onthe V_(D)* and V_(Q)* voltage commands (task 406), and adds ΔI_(Q) toI_(Q)* to obtain the I_(Q)** adjusted current command (task 408).However the torque is reduced as explained in the context of FIG. 3above. To keep the torque linearity, process 400 generates a ΔI_(D)adjusting current command as a function of the ΔI_(Q) adjusting currentcommand (task 410). Then, a torque linearity loop applies a currentadjusting gain K (task 412), multiplies K by the ΔI_(Q) to obtain anoutput current command ΔI_(D) (task 414), and limits the output currentcommand to obtain the ΔI_(D) adjusting current command within a desiredrange (about −30 to about 0 Amps) (task 416). Values of K, and the lowerand upper limits of the limiter are explained above.

Process 400 then adds ΔI_(D) to I_(D)* and the second current command toobtain the I_(Q)** adjusted current command (task 418). ΔI_(D) adjuststhe I_(D)* current command such that the torque linearity remainsconstant as shown in FIG. 4 above while the IPM field is weakened.Process 400 then limits the q-axis and the d-axis currents I_(Q)** andI_(D)** to generate the limited q-axis and d-axis current commandsI_(Q)***, and I_(D)*** (task 419). In turn, I_(Q)*** and I_(D)*** areused as inputs to module 216 for the generation of the voltage commands(V_(D)*, and V_(Q)*). Thereby, the current is suitably regulated toweaken the field in the IPM machine.

Process 400 then generates V_(D)* and V_(Q)* voltage commands based onI_(D)***, I_(Q)***, I_(D) and I_(Q) (task 420).

Process 400 also rotates the IPM machine stator at ω_(R) by deliveringload-driving currents to the motor (task 422). To do this, the V_(AS)*,V_(BS)*, and V_(CS)* stationary frame voltage commands are generatedbased on the V_(D)* and V_(Q)* synchronous voltage commands, to producethe I_(AS), I_(BS) and I_(CS) stationary frame currents. The load isthen delivered via the stationary frame currents to the IPM machine.

With this approach, the torque linearity is maintained in a fieldweakening region of the IPM machine.

While at least one exemplary embodiment has been presented in theforegoing detailed description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or exemplary embodiments are only examples, and arenot intended to limit the scope, applicability, or configuration of theinvention in any way. Rather, the foregoing detailed description willprovide those skilled in the art with a convenient road map forimplementing the exemplary embodiment or exemplary embodiments. Itshould be understood that various changes can be made in the functionand arrangement of elements without departing from the scope of theinvention as set forth in the appended claims and the legal equivalentsthereof.

1. A method for linearizing torque generated by an electric machine, the method comprising: generating, based on d-axis and q-axis voltage commands, a first adjusting current command; multiplying the first adjusting current command by a gain to generate an output current command, wherein the gain is a variable that is influenced by torque and q-axis components of stator current; and limiting the output current command to generate a second adjusting current command.
 2. The method according to claim 1, wherein the gain is calculated based on the relationship ${K = {\frac{4}{3*P} \cdot \frac{T^{*}}{\left( {L_{Q} - L_{D}} \right)I_{Q}^{**{*2}}}}},$ wherein K is the gain, P is number of poles of a machine, L_(D) and L_(Q) are d-axis and q-axis machine inductances respectively, T* is a torque command, and I_(Q)*** is limited q-axis current command.
 3. The method according to claim 1, further comprising: adding the second adjusting current command and a d-axis current command to generate a d-axis adjusted current command.
 4. The method according to the claim 3, further comprising: generating the d-axis and q-axis voltage commands based on the d-axis current command, a q-axis current command, a d-axis feedback current and a q-axis feedback current.
 5. The method according to the claim 4, wherein the step of generating the d-axis and q-axis voltage commands, comprises: generating the d-axis and q-axis voltage commands based on the d-axis adjusted current command, a q-axis adjusted current command, a d-axis feedback current and a q-axis feedback current.
 6. A torque linearity control architecture for an electric machine, the control architecture comprising: a field weakening control loop that generates a first adjusting current command based on d-axis and q-axis voltage commands; a gain module configured to multiply the first adjusting current command by a gain to generate an output current command, wherein the gain is a variable that is influenced by torque and q-axis components of stator current; and a limiter module coupled to the gain module, the limiter module being configured to generate a second adjusting current command by limiting the output current command.
 7. The control architecture according to claim 6, wherein the gain is calculated based on the relationship ${K = {\frac{4}{3*P} \cdot \frac{T^{*}}{\left( {L_{Q} - L_{D}} \right)I_{Q}^{**{*2}}}}},$ wherein K is the gain, P is number of poles of a machine, L_(D) and L_(Q) are d-axis and q-axis machine inductances respectively, T* is a torque command, and I_(Q)*** is limited q-axis current command.
 8. The control architecture according to claim 6, further comprising: a first adder that generates a q-axis adjusted current command based on the first adjusting current command and a q-axis current command.
 9. The control architecture according to claim 8, further comprising: a look-up table module that receives a torque command, a rotor angular velocity, and a DC-link voltage, and that generates the q-axis current command and a d-axis current command.
 10. The control architecture according to claim 9, further comprising: a second adder coupled to the limiter module and configured to receive the second adjusting current command as one input and the d-axis current command as another input, wherein the adder adds the second adjusting current command to the d-axis current command to generate a d-axis adjusted current command.
 11. The control architecture according to the claim 10, further comprising: a synchronous current regulator module that generates the d-axis and q-axis voltage commands based on the d-axis current command, a q-axis current command, a d-axis feedback current and a q-axis feedback current.
 12. The control architecture according to the claim 11, wherein the synchronous current regulator module generates the d-axis and q-axis voltage commands based on the d-axis adjusted current command, a q-axis adjusted current command, a d-axis feedback current and a q-axis feedback current.
 13. The control architecture according to claim 10, further comprising: a phase current module that receives the DC-link voltage, and a rotor angular velocity, and that limits the d-axis and q-axis adjusted current commands, and generates d-axis and q-axis limited current commands.
 14. A method for linearizing torque generated by an electric machine, the method comprising: generating, based on first and second voltage commands, a first adjusting current command; multiplying the first adjusting current command by a gain to generate an output current command, wherein the gain is a variable that is influenced by torque and q-axis components of stator current; and limiting the output current command to generate a second adjusting current command.
 15. The method according to the claim 14, further comprising: generating the first and second voltage commands based on a first current command, a second current command, a first feedback current and a second feedback current.
 16. The method according to claim 15, further comprising: adding the second adjusting current command and the second current command to generate a second adjusted current command.
 17. The method according to the claim 15, wherein the step of generating the first and second voltage commands, comprises: generating the first and second voltage commands based on a first adjusted current command, the second adjusted current command, a first feedback current and a second feedback current.
 18. A torque linearity control architecture for an electric machine, the control architecture comprising: a field weakening control loop that generates a first adjusting current command based on d-axis and q-axis voltage commands; a gain module configured to multiply the first adjusting current command by a gain to generate an output current command; a limiter module coupled to the gain module, the limiter module being configured to generate a second adjusting current command by limiting the output current command; a look-up table module that receives a torque command, a rotor angular velocity, and a DC-link voltage, and that generates a q-axis current command and a d-axis current command; a first adder that generates a q-axis adjusted current command based on the first adjusting current command and the q-axis current command; and a second adder coupled to the limiter module and configured to receive the second adjusting current command as one input and the d-axis current command as another input, wherein the adder adds the second adjusting current command to the d-axis current command to generate a d-axis adjusted current command.
 19. The control architecture according to claim 18, wherein the gain is a constant.
 20. The control architecture according to claim 18, wherein the gain is a variable that is influenced by torque and q-axis components of stator current.
 21. The control architecture according to claim 18, wherein the gain is calculated based on the relationship ${K = {\frac{4}{3*P} \cdot \frac{T^{*}}{\left( {L_{Q} - L_{D}} \right)I_{Q}^{**{*2}}}}},$ wherein K is the gain, P is number of poles of a machine, L_(D) and L_(Q) are d-axis and q-axis machine inductances respectively, T* is a torque command, and I_(Q)*** is limited q-axis current command.
 22. The control architecture according to the claim 18, further comprising: a phase current module that receives the DC-link voltage, and the rotor angular velocity, and that limits the d-axis and q-axis adjusted current commands, and generates d-axis and q-axis limited current commands; and a synchronous current regulator module that generates the d-axis and q-axis voltage commands based on: the d-axis limited current command, the q-axis limited current command, a d-axis feedback current, and a q-axis feedback current. 